Methods which utilize phase separation by emulsion polymerization have heretofore been known to produce particles in the order of submicrometers having various shapes such as DARUMA-shaped (potbellied particles), IIDAKO-shaped (octopus ocellatus-shaped particles), KONPEITO-shaped (a Japanese confectionery with wart-like protrusions over the surface-shaped particles), hollow particles, and other irregularly shaped particles (see Non-Patent Document 1).
On the other hand, as a method for producing porous particles with pores in the order of micrometers, a method comprising causing polymer seed particles to absorb a cross-linking monomer and an initiator, and polymerizing the monomers (see Patent Document 1), and a method comprising adding a mixture of cross-linking monomers to polymer particles, and polymerizing the monomers by heating them rapidly to the decomposition temperature of the initiator in the presence of an oil-soluble initiator (see Patent Document 2) have been known.
Known porous particles with a particle diameter in the order of micrometers, however, have low porosity and a wide particle-size distribution and are not monodispersed, and therefore have not been practical.
Thus, porous particles which have high porosity and a narrow distribution have been required for use as a carrier for pigments or pharmaceutical agents, or for use as various types of adsorbents, analytical columns, and the like.
Moreover, colored resin particles produced by staining resin particles with a dye have problems of poor color developing stability and the like. A method of coloring resin particles with a pigment has been regarded as a preferable method for overcoming such a problem.
Among the methods for coloring resin particles with a pigment, Patent Document 3 reported a method of preparing a pigment-containing monomer by suspension polymerization, and Patent Documents 4 and 5 proposed polymerized toners. The colored resin particles obtained by these methods, however, had a wide particle-size distribution, and were not monodispersed.
Moreover, Patent Document 1 reported a method comprising preparing porous particles as resin particles, and adding a pigment to the porous particles. The pigment, however, was not easily agglomerated in the porous particles obtained by this method, and the amount of pigment contained therein was small.
Patent Document 1: JP 2000-191818 A
Patent Document 2: JP 1986-225254 A
Patent Document 3: JP 2004-4506 A
Patent Document 4: JP 2004-271816 A
Patent Document 5: JP 2004-226449 A
Non-Patent Document 1: M. Okubo et. al., Colloid Polym. Sci., 274:433-438 (1996)